OBJECTIVE: To determine mortality trends from hypertension in Mexico nationwide, by state, by socioeconomic region, and by sex and to establish an association between education, state of residence, and socioeconomic region with mortality from hypertension in 2000-2008. METHODS: Records of mortality associated with hypertension for 2000-2008 were obtained from the National Information System of the Secretariat of Health. This information is generated by the National Institute of Statistics, Geography and Informatics through death certificates issued throughout the country. International Classification of Diseases, 10th Revision, codes corresponding to the basic cause of death from hypertension were identified. Rates of mortality nationwide, by state, and by socioeconomic region were calculated. The strength of association (obtained by Poisson regression) between states where individuals resided, socioeconomic regions, and education with mortality from hypertension was determined. The seven socioeconomic regions were elaborated by the National Institute of Statistics, Geography and Informatics and include the 31 states and Mexico City according to indicators that are related to well-being such as education, occupation, health, housing, and employment. RESULTS: Individuals who did not complete elementary school had a higher risk of dying from hypertension than people with more or no education [relative risk (RR) 1.462, 95% confidence interval (CI) 1.442-1.482]. Mexico City, Oaxaca, and region 7 had the strongest association with dying from hypertension [Mexico City: RR 2.6, CI 2.1-3.2 (2000) and RR 2.5, CI 2.1-3.1 (2005); Oaxaca: RR 2.4, CI2.0-3.0 (2006) and RR 2.7, CI2.3-3.3 (2008); region 7: RR 1.58, CI 1.45-1.72 (2000) and RR 1.25, CI 1.17-1.34 (2008)]. CONCLUSIONS: Age-adjusted mortality rates per 100 000 inhabitants who died from hypertension increased from 15.7 to 18.5 between 2000 and 2008, taking the world population age distribution as standard. Mortality was higher in women than in men and in individuals who did not complete elementary school than in those with more or no education. The strongest associations were in Mexico City, Oaxaca, and region 7.

Hypertension is a worldwide public health problem, with an estimated 972 million hypertensive people in 2000. Of this total, 333 million live in industrialized countries and 639 live in developing countries. In the same year, 26.4% of the adult population age 20 years or older in the world were identified with hypertension (1).

In the United States, at least 65 million hypertensive patients age 18 years or older were detected in 1999-2000. Of them, 35 million were women and 30 million were men. The total prevalence in those years was 31.3%. The total expenditure for hypertension in that period was $110 billion (2).

In Mexico, hypertension represents a public health problem; in 2000, the National Health Survey identified approximately 15 million hypertensive patients age 20 years or older (3), and the trend is increasing (4). Also, the survey showed that more than half of the population with hypertension were not aware of it. Of the patients who knew about their disease, fewer than half took medication, and the disease was controlled in only about 20% of them (3).

The increased morbidity from hypertension in Mexico could be related to the epidemiological transition that is taking place there, which is characterized by a gradual substitution of deaths due to transmissible causes with a pattern of a prevalence of chronic degenerative diseases like diabetes and cardiovascular disorders (5, 6).

The epidemiological transition has resulted in a longer life expectancy, which in turn results in greater economic development, better social organization, and industrialization (7).

At a given moment in the world, several countries, and even distinct regions in the same country, reveal different stages of epidemiological transition. This is also true for Mexico (7, 8).

The epidemiological transition has brought changes in the lifestyle of the population, which has contributed to an increase in some factors associated with hypertension, such as diabetes mellitus, smoking, hypercholesterolemia, obesity, and a sedentary lifestyle (6, 8-13).

Hypertension is defined as having a systolic blood pressure > 140 mmHg and/ or a diastolic blood pressure > 90 mmHg on the first reading and confirmed by a second reading. Hypertension is a chronic degenerative disease that can produce complications such as cardiac failure, renal failure, blindness, and cerebral vascular disease among others (14, 15). Hypertension represents an important economic burden for health systems due to government expenditures in treating the disease as well as its complications (16).

The objectives of this study are to determine mortality rates nationwide, by state, by socioeconomic region, and by sex and to establish the strength of association between education, state of residence, and socioeconomic region with mortality from hypertension in 2000-2008.

MATERIALS AND METHODS

An ecological study design was used. Mortality records associated with hypertension for 2000-2008 were obtained from the National Information System of the Secretariat of Health of Mexico (17). This information is generated by the National Institute of Statistics, Geography and Informatics, and it is collected from death certificates issued nationwide. All individual records of mortality in which the basic cause of death was hypertension in the period 2000-2008 were included in the study. The codes of the International Classification of Diseases, 10th Revision (18), were identified. They corresponded to the basic cause of death from hypertension such as: I10 essential or primary hypertension, I11 hypertensive cardiac disease, I12 hypertensive renal disease, I13 hypertensive cardiorenal disease, and I15 secondary hypertension.

Raw and age-adjusted mortality rates nationwide per 100 000 inhabitants were obtained, taking the world population as the standard population (19, 20). Age-adjusted mortality rates per 100 000 inhabitants from each state and from each of the 7 socioeconomic regions (Table 1) established by the National Institute of Statistics, Geography and Informatics were also obtained (21). The national population, estimated by the National Population Council for 2000-2008 (22), was used for the rate adjustment. The relative risk (RR) and 95% confidence interval (CI) for mortality from hypertension for each of the seven socioeconomic regions and each state of residence were calculated by Poisson regression.

The seven socioeconomic regional categories for Mexico have been defined by the National Institute of Statistics, Geography and Informatics in which differences observed in the social and economic conditions of the population throughout Mexico are presented according to the XII General Population and Housing Census. The seven socioeconomic socioeconomic regions comprise the 31 states and Mexico City according to indicators related to well-being such as education, occupation, health, housing, and employment. States classified in the same region have similar characteristics on average; that is, they are homogenous, while the regions differ from one another. Region 7 shows the states with the most favorable socioeconomic conditions according to the indicators used. Region 1 includes states with the least favorable socioeconomic conditions.

The methodology used to establish the regions had the objective of forming strata with minimal variance in an effort to group the elements more alike or closer to each other following a criterion of established similarity, which allows for differentiating one region from another. Among the techniques used are Mahalonobis distances and a combination of factorial analysis and the algorithm of the K-means (21).

The Poisson regression model was chosen to determine the strength of association between states, socioeconomic regions of residence, and education with mortality from hypertension, because as a dependent variable, the number of deaths has a Poisson distribution that takes positive whole values. Poisson regression is equivalent to a logarithmic regression of mortality rates. The exponential coefficients allow for estimation of the RR of dying (23).

Registrations were handled by the Access 2003 program; all data were transferred to the Number Cruncher Statistical System program 2001 (24), with which the strength of association between each state and socioeconomic region of residence and mortality from hypertension was obtained by Poisson regression. The Epidat version 3.1 program was used to determine ageadjusted mortality rates by state and socioeconomic region.

RESULTS

From 2000 to 2008, 109 807 individuals died of hypertension in Mexico. During that time, the age-adjusted rate standardized per 100 000 inhabitants increased from 15.7 to 18.5; deaths in women predominated (Table 2).

The strength of association between education and death from hypertension was determined. Individuals who did not complete elementary school showed a higher risk of dying (RR 1.462, CI 1.442-1.482), while subjects with a higher education level had a lower risk of dying, as is the case for those with a college education (RR 0.121, CI 0.117-0.125) (Table 3).

The strength of association between each state of residence and death from hypertension in 2000-2008, was determined by Poisson regression, taking Yucatan, one of the three states with less mortality from hypertension in the study period, as a reference. The strongest associations were in Mexico City and Oaxaca [Mexico City: RR 2.6, CI 2.1-3.2 (2000) and RR 2.5, CI 2.1-3.1 (2005); Oaxaca: RR 2.4, CI 2.0-3.0 (2006) and RR 2.7, CI 2.3-3.3 (2008)] (Table 6).

In the study period, the state with the lowest strength of association with mortality from hypertension was Quintana Roo [RR 0.5, CI 0.3-0.8 (2000) and RR 0.7, CI 0.5-0.9 (2008)] (Table 6).

The strength of the association between each socioeconomic region of residence and death from hypertension was also determined by Poisson regression, taking as reference region 1; region 7 presented the strongest association with mortality from hypertension [RR 1.58, CI 1.45-1.72 (2000) and RR 1.25, CI 1.17-1.34 (2008)] (Table 7).

Hypertension has significantly increased in Mexico over the past 20 years (4). In 2000, the mortality rate per 100 000 inhabitants standardized with the distribution of the world population was 15.7 and increased to a rate of 18.5 in 2008 (Table 2). Mortality rates from hypertension will possibly continue to increase since, according to estimates by Kearney, the prevalence of hypertension will rise to 60% from 2000 to 2025 throughout the world, and it is predicted that it will amount to nearly 1 580 million hypertensive individuals. In comparison, in Latin America in 2000, 60 million men and 54.3 million women with hypertension were identified, and it is projected that by the year 2025, there will be 102.1 million men and 98.5 million women with hypertension (1).

In Mexico, in the period 2000-2008, 109 807 individuals died from hypertension. The mortality was higher in women than in men (Table 2). It has been observed that there are factors related to the development of hypertension in women, such as menopause, which produces increased sensitivity to salt. There is also evidence that oral contraceptives can enhance the risk of hypertension in women.

Advanced age could enhance mortality from hypertension in women compared with men. The prevalence and severity of hypertension increase markedly with advancing age in women, so that a higher percentage of women than men have high blood pressure after age 65 years. Furthermore, controlling hypertension is more difficult to achieve in older women. Data from the Framingham Heart Study showed gender differences in blood pressure control rates and in the pattern of antihypertensive medications prescribed. An age-related decrease in blood pressure control rates was more pronounced in women than in men. Among the oldest participants with hypertension, only 23% of women (vs. 38% of men) were controlled to a blood pressure of 140/90 mmHg. It is unknown whether the age-related decline in blood pressure control among women is related to true treatment resistance because of biological factors or to inappropriate drug choices in the clinical setting (25, 26).

Mortality from hypertension was higher in individuals with a low education level (Table 3). Education level is a socioeconomic indicator of health, for it has been observed that persons with more education have more possibilities of being employed and therefore of having better incomes and consequently greater well-being, which directly affects their health. In addition, persons with a higher education level (4 more years of schooling) are less likely to smoke (11 percentage points relative to a mean of 23%), to drink a lot (7 fewer days of 5 or more drinks in a year, among those who drink, of a base of 11 days), and to be overweight or obese (5 percentage point lower obesity, compared with an average of 23%). Among individuals with chronic conditions, such as diabetes and hypertension, the more educated are more likely to have their condition under control. Evidence suggests that a higher education level is associated with a lower risk of having hypertension (27-30).

The states that presented the strongest association with mortality from hypertension were Mexico City (2000-2005) and Oaxaca (2006-2008) (Table 6). On the other hand, Mexico City as region 7 presented the strongest association with mortality from hypertension in the period of study (Table 7). Factors such as obesity, sedentary lifestyle, and stress could be associated with a higher risk of dying from hypertension in this region.

Mexico City has a very low degree of marginality, which implies a better economic situation (Table 1). The latter is a result of changes and technological innovations. Some of these changes reduce physical activity of individuals and produce modifications in their eating habits (30-32), which could favor obesity and thereby increased morbidity and mortality from hypertension (33, 34).

The results of the National Health and Nutrition Survey showed that the urban population has a higher prevalence of obesity than the rural population. Mexico City presented the highest prevalence of obesity in the adult population together with the northern states of the country (35). In Mexico City, a prevalence of obesity (body mass index > 30 kg/m2) of 41% in women and 27% in men has been found (36). Obesity is associated with hypertension, and it represents a strong predictor of cardio-vascular-related mortality (37, 38).

Sedentary lifestyle is another factor associated with hypertension, as it is linked to obesity (39). It has been identified with higher frequency in urban areas than in rural ones, and it could be contributing to morbidity and mortality from hypertension in region 7 (40-42). In this region, sedentary lifestyle has a very high prevalence in the population: 71% of men and 82% of women (36). Regular physical activity is inversely associated with development of hypertension. Regular physical activity avoids insulin resistance and keeps individuals at a normal weight. These benefits could be contributing to prevent hypertension (43).

Frequently, it has been observed that individuals from urban areas have more stress than those from rural areas (44), and there is evidence that stress is associated with the development of hypertension. The mechanisms by which stress could cause hypertension are an increase in vascular reactivity and slow poststress recovery (45).

States with a greater well-being, according to the classification by socioeconomic regions of the National Institute of Statistics, Geography and Informatics (Table 1), comprise those that constitute region 7. This region presented one of the highest mortality rates as well as the strongest association with mortality from hypertension, whereas the states that form regions 2-6 presented a similar strength of association with mortality from hypertension but lower than that of region 7 (Table 7).

Mexico is in distinct stages of the epidemiological transition process; at the same time, it has great disparities in health services, education, employment, and personal incomes. These factors could affect mortality from hypertension (29, 30, 46).

This study observed that mortality from hypertension is high, with an increasing trend. Mexico City as a state and as region 7 presented one of the highest mortality rates and the highest risk of dying from this disease in the period of study. Therefore, it is important to emphasize preventive measures such as healthy nutrition and physical activity. It is also necessary to improve medical attention in order to detect hypertension promptly and to treat complications in an efficient way, thereby improving the quality of life and decreasing mortality in these individuals. The preceding could be accomplished by applying multisectoral programs in which health and education institutions promote healthy nutrition and appropriate physical activity and discourage obesity.

Applying government policies aimed at regulating the media in referring to unhealthy food and promoting physical activity, preventing development of the disease in groups at risk, and improving blood pressure monitoring in individuals already ill is strongly indicated.

The limitations of this paper lie in the fact that hypertension is a risk factor for cardiovascular disease in general and not only for cardiac, renal, and cardiorenal diseases. It is also associated with cerebral hemorrhage, myocardial infarction, and arrhythmias, although these entities were not evaluated because there are no codes in the International Classification of Diseases, 10th Revision, with a specific category for hypertension and the three diseases. In addition, in Mexico in the period 1999-2001, an underregistration of deaths of 13.7% was identified (47); therefore, the mortality and the strength of association in some states and socioeconomic regions could be higher.

CONCLUSIONS

In Mexico, from 2000 to 2008, the mortality rate from hypertension increased from 15.7 to 18.5 per 100 000 inhabitants. Women exhibited higher mortality than men. Individuals who did not complete elementary school presented a higher risk of dying from hypertension (RR 1.462, CI 1.442-1.482) than those who had no school. The states with the strongest association with mortality from hypertension were Mexico City from 2000 to 2005 and Oaxaca from 2006 to 2008. The socioeconomic region with the strongest association with mortality from hypertension was region 7.